This invention deals with integrated microphonic suppression means for a resonant cavity. The cavity resonator of the invention is utilized as a frequency determining element in a semiconductor oscillator to produce high power radio energy at VHF/UHF frequencies.
In an RF oscillator employing a gas filled cavity resonator, microscopic dimensional changes resulting from external shocks and vibrations will cause undesired RF frequency deviations (microphonics). In the past microphonics have not been a serious problem since most VHF/UHF oscillators have utilized stripline transmission lines as resonating elements. Because of the relatively low Q value of stripline transmission lines, these devices give spurious sideband noise performance that is unacceptable in many high power RF oscillator applications. Cavity resonators offer much better performance characteristics than stripline resonators when used with RF oscillators at VHF/UHF frequencies. Unfortunately cavity resonators, when coupled to RF oscillators, are very susceptible to microphonics.
In a coaxial cavity resonator used in a RF oscillator the dimensions most sensitive to microphonics are (1) the tuning screw penetration into the resonator, (2) the gap between the tuning screw and the resonator center conductor, and (3) the gaps between the center conductor and the coupling probes. The invention yields a cavity resonator having negligible microphonics while maintaining a satisfactory quality factor. An RF oscillator using this type of cavity as a resonating device will exhibit low residual FM hum and noise under shock and vibration conditions, while maintaining the superior sideband performance inherent in a high Q cavity resonator oscillator.
It is an object of this invention to limit the mechanical displacements in a cavity resonator oscillator: specifically limiting displacements between the tuning screw, coupling probes and resonator center conductor to acceptable levels and thereby minimizing the effects of microphonics.
It is a further object of this invention to maintain acceptable RF performance of the cavity oscillator while simultaneously limiting the mechanical displacements of the various oscillator component parts.